Integrated circuit devices typically display sensitivity to electrostatic discharge (ESD) events thus making it necessary to take measures to protect these circuits. I/O circuits may either be protected by providing separate ESD protection structures or, preferably, providing for ESD self-protection of the I/O drivers. One common way of protecting BiCMOS circuits is through the use of BJT devices. However, a critical consideration for a triggering structure, whether it be a BJT or GGNMOS or any other triggering structure, is the anode current distribution near the junction breakdown region. In the case of GGNMOS, one approach adopted to improve current spreading is to make use of a so-called ballasting region that serves as a saturation resistor. The ballast region of a GGNMOS typically comprises an extended, unsilicided, drain region. This has the effect of not only limiting the total current but also provides for local current density stabilization.
However, as the dimensions of structures continues to be reduced, the resistance provided by the ballasting region is also reduced. Furthermore, there is a need not to add costs by having to introduce additional process steps. One solution for addressing this issue in the case of GGNMOS is presented in a previously filed application owned by the same assignee as the present invention, which makes use of a partially blocked ballasting region to provide a comb-like ballasting region.
The present invention provides for current stabilization in the case of BJT devices.